THE NBEVOUS SYSTEM
pollicis and contrahentes. Hepburn points out ulnar nerve supplies the fourth lumbrical in the Chi panzee, the third and fourth lurnbricales in the Orang and Gibbon, and the second, third and fourth muscles in the Gorilla.
The internal cutaneous nerves of the arm and forearm and the intercosto-brachial nerves are much as in Man.
The musculo-spiral nerve courses as in Man. In the arm it supplies the skin, triceps and dorso-epi-trochlearis. In the lower part of the arm it supplies the brachialis anticus in the Gorilla alone. At the bend of the elbow it supplies the muscles rising from the external condyle of the humerus, and divides into the radial and posterior interosseous nerves. These have the same course and distribution as in Man, and the latter may supply the pronator quadratus and wrist-joint.
The musculo-cutaneous nerve has the same course and distribution as in Man. The circumflex nerve is also similar.
THE LUMBAR AND SACBAL PLEXUSES.
These plexuses, which are formed by the anterior divisions of the lumbar and sacral nerves, are united by the lumbo-sacral cord. The formation of the nerves springing from them is liable to considerable individual variation. The mode of formation in the Chimpanzee is shown in fig. 56. And the origins of the nerves as recorded by various observers are shown in the following list:— «